The present invention generally relates to fuel-fired fluid heating devices and, in a representatively illustrated embodiment thereof, more particularly provides a fuel-fired water heater having a dual tank structure and a specially designed dual pass condensing type heat exchanger incorporated therein.
Conventional fuel-fired water heaters are typically of a “single pass”, non-condensing configuration, meaning that the hot combustion gases used to heat the tank-stored water are subjected to only a single pass through a heat exchanger structure (usually a vertical flue) within the tank before being discharged from the water heater to, for example, an external vent structure, and that flue gas condensation does not occur to any appreciable degree in the heat exchanger structure within the water heater tank. In this conventional type of fuel-fired water heater, the overall thermal efficiency is typically limited to about 80-85%. Various proposals have been made to provide fuel-fired water heaters with condensing type single-pass heat exchangers (i.e., in which flue gases condense within the heat exchanger). However, previously proposed single-pass condensing type heat exchange structures incorporated in fuel-fired water heaters typically provide the water heaters with thermal efficiencies limited to the 85-90% range.
In an attempt to increase this thermal efficiency to above 95%, multi-pass condensing heat exchangers of varying configurations and types have been proposed for installation within the tank portions of fuel-fired water heaters. While such previously proposed multi-pass condensing type heat exchangers have met this thermal efficiency goal, they have also undesirably presented various problems, limitations and disadvantages. These include increased heat exchanger complexity, higher material and fabricational costs, condensate management problems, increased operational noise, and reduced heat exchanger operational life.
It would thus be desirable to provide a fuel-fired water heater, or other type of fuel-fired fluid heating device, with an improved multi-pass condensing type heat exchanger. It is to this goal that the present invention is primarily directed.